/// 引用(安全的指针): &T  &mut T
/// 原始指针: *const T, *mut T
/// 智能指针: 具有与之相关联的额外元数据和代码，超出作用域时能够自动释放底层资源 (Drop/Deref特征)
fn main() {

    let a = &56_u32;
    let a_raw_ptr = a as *const u32;

    let b = &mut 5.21;
    let b_mut_ptr = b as *mut f64;

}